The ability of the Raman technique to acquire a complete spectrum at each pixel of the sample allows for the generation of Raman maps, or images, that reveal the composition, structure, and distribution of different chemicals in the sample without the use of exogenous labels. As a powerful optical imaging technique, Raman imaging microscopes are in high demand in laboratories and factories for applications including pharmaceutics, forensics, materials and life sciences.
Existing methods of acquiring Raman spectra with a charge-coupled device (CCD) from multiple sources are limited to the sources being aligned in a line. The sources would be arranged so that the signal from each source would be detected by different pixel rows of the CCD. Thus overlap and cross-talk, a problem for Raman spectroscopy due to its generally weak signal strength, would be avoided. In this method however, the number of sources (i.e., samples) for parallel acquisition is limited by the number of pixel rows, usually the vertical dimension, of the CCD. More than one source in a single pixel row would result in a signal with too much cross-talk and the spectra from each source could not be separated. In one example, laser tweezers Raman spectroscopy (LTRS) has been proven useful for analyzing individual cells without need for exogenous labels or extensive sample preparation and perturbation. The utility though would be even greater if cells did not need to be arranged in a single line thereby allowing more cells to be analyzed in a single sample. Additionally, the time-sharing technique that uses only one laser focus makes it difficult to trap a larger number of microparticles (>50).
Furthermore, for current high-resolution confocal Raman imaging products, a single laser focus needs to be scanned point by point in both x- and y-directions to acquire Raman spectra from every pixel, and it will take tens of minutes or hours to form one frame of a Raman image. On the other hand, by using line illumination, line-scan Raman imaging products enable a fast imaging speed with a reduced measurement time of seconds or minutes. However, a line-scan Raman microscope has poor spatial resolution in the line-scan direction compared with the single point scanning confocal Raman microscope. The improvement in imaging speed of the line-scan technique requires a sacrifice in the spatial resolution of the image.